After you've finished up the main quest for burning down the Chapel in Chapter one ShantyTown. You'll be put back in your safe-social hub, the Black Hand camp as per usual.
Go and have a chat with fox, the only female in this camp, and she'll inform you of a bloodjaw. You have the choice to help out or not, offer to take up this task and you'll be transported to the area automatically like most side quests.
Once you're in the area, it's linear, just head forwards killing all the enemies in your way, which at the very end of this not-so-large area, you'll see a woman surrounded by inquisition soldiers, kill them all and save her. Activating a line of dialogue which completes this quest and nets you the trophy.